Have you selected "* All Defined Characters" in the combo box on the toolbar for these fonts? The characters in those fonts can be defined within a Unicode subrange that is not selected currently in the combo box on the toolbar. (Or we can answer in more details if you send us one or both fonts to support @ proximasoftware.com.)

The screenshot with the FontExpert Characters Table of smallest size for
previewed font is known for me.

Usually it happens when the font was loadeded (installed) and then it's font file was deleted or moved , but it seems some program running at that time (e.g. Microsoft Word) "keeps" this font in memory (while the font file actaully was uninstalled or moved to another place).